Chewing gum base is conventionally prepared using a batch mixer, for example, a sigma blade mixer, using a mixing time of about one to four hours per batch. Typically, predetermined amounts of elastomer, elastomer plasticizers and fillers are added to a heated sigma blade mixer having a front to rear blade speed ratio of about 2:1. After the initial ingredients have massed homogeneously, a balance of elastomer plasticizer, filler, softeners/emulsifiers, waxes (when used) and other ingredients are added sequentially to the batch mixer and blended until a homogeneous mass is attained. The final mass temperature can be between 60.degree. C. and 150.degree. C., preferably between 80.degree. C. and 120.degree. C. The completed molten mass is emptied from the mixing kettle into coated or lined pans, extruded or cast into any desirable shape and allowed to cool and solidify.
The foregoing batch process, which operates under conditions of low shear and little or no pressure, has been very effective in providing well-mixed chewing gum bases, with little or no degradation of the gum base components occurring during mixing. However, the process has the disadvantage of requiring a long mixing time. Also, because the process involves batch mixing, not at steady state, there may be small but detectable variations in color, consistency or taste between different batches.
In order to shorten the mixing time and eliminate variations between batches, consideration has been given to mixing gum base continuously. However, most known continuous mixing processes, for example, twin screw extruders, have been difficult to use successfully because their residence time is too short, i.e., on the order of a few minutes. This extreme shortening of residence time has made it difficult to produce a homogeneous gum base without lumps, islands, and other inconsistencies.
Ehrgoot et al. U.S. Pat. No. 3,995,064, discloses the concept of making chewing gum base continuously. To accomplish this, the gum base must be exposed to some mixing under high intensity and shear, in order to disperse the elastomer. However, high shear mixing may increase the amount of degraded gum base ingredients in the product. Also, the reference recommends using a number of separate preblending operations to help achieve product homogeneity.
French Publication No. 2,635,441, to Boudy, discloses making a gum base concentrate using a continuous process. Polymers, plasticizers and fillers are introduced into different sleeves of a twin screw extruder having a residence time not exceeding 1.5 minutes. The twin screw extruder includes a region of high shear mixing to help disperse the ingredients. Later, the gum base premix is combined with other gum base ingredients using a separate process.
European Publication No. 0,273,809, to Horst, discloses a process for making a chewing gum base using an industrial mill. Elastomer and filler are fed to the mill, heated, and mixed for 35 to 75 minutes, to produce a gum base premix. The premix is then discharged from the mill, fragmented, and combined with other gum base ingredients using a powder mixer.
Witzel et al. U.S. Pat. No. 4,217,368, and Friello et al. U.S. Pat. No. 4,208,431, disclose standard batch gum base processes using sigma blade mixers. D'Amelia et al. U.S. Pat. No. 4,968,511, discloses a direct one-step process for making chewing gum without the intermediate step of forming a chewing gum base, using a specific mixture of ingredients.
Notwithstanding the foregoing efforts, there remains a need or desire in the chewing gum industry for an effective method of making a chewing gum base continuously, to save time and eliminate inconsistencies between batches, without using high shear or employing multiple preblending steps.